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Message-Id: <20070821.000404.39159401.davem@davemloft.net>
Date: Tue, 21 Aug 2007 00:04:04 -0700 (PDT)
From: David Miller <davem@...emloft.net>
To: torvalds@...ux-foundation.org
Cc: csnook@...hat.com, piggin@...erone.com.au, satyam@...radead.org,
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Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all
architectures
From: Linus Torvalds <torvalds@...ux-foundation.org>
Date: Mon, 20 Aug 2007 22:46:47 -0700 (PDT)
> Ie a "barrier()" is likely _cheaper_ than the code generation downside
> from using "volatile".
Assuming GCC were ever better about the code generation badness
with volatile that has been discussed here, I much prefer
we tell GCC "this memory piece changed" rather than "every
piece of memory has changed" which is what the barrier() does.
I happened to have been scanning a lot of assembler lately to
track down a gcc-4.2 miscompilation on sparc64, and the barriers
do hurt quite a bit in some places. Instead of keeping unrelated
variables around cached in local registers, it reloads everything.
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